Treatment processes for superalloy articles and related articles

ABSTRACT

A treatment process for treating an article including a superalloy having a degraded microstructure is presented. The process includes subjecting the article to a first heat-treatment including successively heating and cooling the article between a low-end temperature and a high-end temperature and subjecting the article to a second heat-treatment at a solution annealing temperature in a range of from about 80 degrees Fahrenheit below a gamma-prime solvus temperature of the superalloy to about 80 degrees Fahrenheit above the gamma-prime solvus temperature of the superalloy after performing the first heat-treatment. The low-end temperature is in a range of from about 1000 degrees Fahrenheit to about 1800 degrees Fahrenheit and the high-end temperature is in a range of from about 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit.

BACKGROUND

Embodiments of the present disclosure generally relate to treatmentprocesses for recovering desired properties of degraded superalloyarticles. More particularly, embodiments of the present disclosure aredirected to treatment processes applicable to single crystal anddirectionally solidified superalloy articles.

Directional solidification (DS) and single crystal (SX) superalloys havebeen widely used to produce turbine components, for example blades ofaero-engines because of their excellent high-temperature mechanicalproperties. Although, the usage of DS and SX superalloys enablesimproved efficiency and increased creep life as compared to that ofequiaxed polycrystalline superalloys, the DS and SX superalloycomponents may accumulate damage or deform under creep andthermo-mechanical fatigue in the high-temperature operatingenvironments. The degradation of the microstructure occurs typically dueto degraded gamma and gamma-prime phases, which causes significantreduction in desirable mechanical properties and necessitatesreplacement of the components. Instead of completely replacing thedamaged component with a new component, it is often economically viableto repair or refurbish the damaged component for further use.

During refurbishment, the degraded superalloy components are typicallysubjected to a solution heat-treatment process. This solutionheat-treatment may lead to undesirable recrystallization in regions(often, surfaces of the article) of the DS and SX superalloy components,which were subjected to high stresses and/or plastic strains duringmanufacturing. This recrystallization alters and damages themicrostructure of the DS and SX superalloy components, and causesunacceptable material weakening.

Several attempts have been made to inhibit the generation ofrecrystallization such as adjusting manufacturing process by avoidingplastic deformation before solution heat-treatment processing, usingmodified heat-treatment processing, applying coatings on portions of thecomponents for inhibiting recrystallization, generating asecondary-phase in the superalloy for pinning the recrystallizationboundaries to hinder recrystallization, surface oxidation etc.

There continues a need for improved and alternative treatment processesfor the DS/SX superalloy components for recovering desired mechanicalproperties and achieving controlled and/or reduced recrystallization.

BRIEF DESCRIPTION

Provided herein are processes for treating articles comprisingsuperalloys. In one aspect, a treatment process includes heat-treatingan article including a superalloy having a degraded microstructure. Theheat-treatment includes subjecting the article to a first heat-treatmentincluding successively heating and cooling the article between a low-endtemperature and a high-end temperature, wherein the low-end temperatureis in a range of from about 1000 degrees Fahrenheit to about 1800degrees Fahrenheit and the high-end temperature is in a range of fromabout 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit; andsubjecting the article to a second heat-treatment at a solutionannealing temperature in a range of from about 80 degrees Fahrenheitbelow a gamma-prime solvus temperature of the superalloy to about 80degrees Fahrenheit above the gamma-prime solvus temperature of thesuperalloy after performing the first heat-treatment.

In another aspect, a treatment process includes heat-treating an articleincluding a superalloy having a degraded microstructure, theheat-treatment includes subjecting the article to a first heat-treatmentincluding successively heating and cooling the article at least twotimes between a low-end temperature and a high-end temperature, whereinthe low-end temperature is in a range of from about 1300 degreesFahrenheit to about 1600 degrees Fahrenheit and the high-end temperatureis in a range of from about 1900 degrees Fahrenheit to about 2100degrees Fahrenheit and subjecting the article to a second heat-treatmentat a solution annealing temperature in a range of from about 80 degreesFahrenheit below a gamma-prime solvus temperature of the superalloy toabout 80 degrees Fahrenheit above the gamma-prime solvus temperature ofthe superalloy after performing the first heat-treatment. The processfurther includes cooling the heat-treated article from the solutionannealing temperature with a cooling rate higher than 50 degreesFahrenheit/minute.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a scanning electron micrograph of an originally prepared SXsuperalloy component.

FIG. 2 is a scanning electron micrograph of the SX superalloy componentafter it has been used in high-temperature service environment forseveral hours.

FIG. 3 is flow chart of a treatment process in accordance with oneembodiment of the treatment processes described herein.

FIG. 4 is a temperature-time profile of a treatment process inaccordance with one embodiment of the treatment processes describedherein.

FIG. 5 is a temperature-time profile of a treatment process inaccordance with another embodiment of the treatment processes describedherein.

FIG. 6 is a scanning electron micrograph of a portion of a treatedarticle that has been undergone a conventional treatment process.

FIG. 7 is a scanning electron micrograph of a portion of a treatedarticle that has been undergone a treatment process in accordance withone embodiment of the treatment processes described herein.

FIG. 8 is a scanning electron micrograph of a portion of a treatedarticle that has been undergone a treatment process in accordance withanother embodiment of the treatment processes described herein.

DETAILED DESCRIPTION

The disclosure generally encompasses treatment processes that can beperformed on superalloy articles, and particularly DS and SX superalloyarticles for recovering their mechanical properties. As used herein, theterm “DS superalloy article” refers to an article that is originallyprepared by a method including directional solidification of asuperalloy. The term “SX superalloy article” refers to an articleoriginally prepared by a method that involves casting from a superalloyin single crystal form. An originally prepared article is usually castfrom a superalloy in single crystal form or directionally solidifiedform followed by the solution heat treatment. Commonly known superalloysinclude gamma-prime strengthened nickel-based, cobalt-based andiron-based superalloys. Typically, in nickel-based superalloys, one ormore of chromium, tungsten, molybdenum, iron and cobalt are principalalloying elements that combine with nickel to form a base matrix, andone or more aluminum, titanium, tantalum, niobium, and vanadium areprincipal alloying elements that combine with nickel to form desirablestrengthening precipitates such as gamma-prime phase i.e., Ni₃(Al, X)and/or gamma-double-prime phase i.e., Ni₃(Nb, X), where X can be one ormore of titanium, tantalum, niobium and vanadium.

The present processes are generally applicable to articles that operatewithin environments characterized by relatively high temperatures, forexample higher than 1000 degrees Fahrenheit and subject to severethermal stresses and thermal cycling. Such operating environments mayalso be referred to as high-temperature service environments. Examplesof such articles include turbine components, for example blades,shrouds, combustor liner, vanes, and augmenter hardware of turbineengines. It is understood that articles other than turbine componentsthat are cast from a superalloy in single crystal form or directionallysolidified form, are considered to be within the scope of the presentdisclosure.

As discussed previously, use of a superalloy article under thehigh-temperature service environments leads to creep deformation andhence degraded or rafted microstructure. This degraded or raftedmicrostructure typically results in reduction of the superalloy strengthand ductility. As used herein, the term “degraded microstructure” refersto a microstructure of an article including a superalloy, which has beenused under the high-temperature service environment. In someembodiments, the degraded microstructure exhibits degraded gamma-primephase in the microstructure of the article including the superalloy.FIG. 1 shows scanning electron micrograph (SEM) of a portion of anoriginally prepared SX superalloy component. The microstructure of theoriginally prepared SX superalloy component exhibits uniformlyprecipitated gamma-prime (Ni₃Al) phase in the nickel matrix. FIG. 2shows SEM of a portion of the degraded component after the SX superalloycomponent has been used under the high-temperature service environmentof a turbine. Deformation due to creep during use led to distortion ofthe gamma-prime phase in the form of ‘rafts’ (as shown in FIG. 2).

Moreover, the superalloy articles include mechanically deformedportions, for example the dovetail portion of a turbine blade. Often,the superalloy articles are subjected to post-solidification processingsteps, such as grinding, polishing, shot peening, and grit blasting, toachieve near-net shape during manufacturing. Such processing steps canproduce localized elastic residual stresses and/or increased dislocationdensity in the microstructure of the superalloy article. As used herein,the term “mechanically deformed portions” refers to portions of thesuperalloy articles that have undergone plastic deformation and exhibitelastic residual stresses and/or high dislocation density due to plasticstrains.

As noted, a typical recovery process involves a solution heat-treatmentabove the gamma-prime solvus temperature to dissolve the degradedgamma-prime phase and then precipitate a refined gamma-prime phase inorder to recover the microstructure and the desired mechanicalproperties of the superalloy article. Though the conventional recoveryprocesses are effective in restoring or recovering gamma-prime phasesand desirable mechanical properties, the mechanically deformed portionsmay undergo excessive recrystallization in a surface area (typically ina depth of less than 0.05 inches, and more particularly less than 0.01inch from the surface of the article) upon exposure to elevatedtemperatures, particularly when the temperature exceeds the gamma-primesolvus temperature of the superalloy during the recovery processes.

As discussed in detail below, provided herein are improved processes fortreating articles including DS or SX superalloys having degradedmicrostructure. The described embodiments provide treatment processesfor achieving the optimal gamma-prime phase while inhibiting orcontrolling the generation of recrystallization in the mechanicallydeformed portions of the treated articles. More particularly,embodiments of the disclosed processes provide controlled and/or reducedgrain size (average grain size<100 microns) of the recrystallized grainsin the mechanically deformed portions of the treated articles. Thetreated articles may also be referred to as rejuvenated articles.

In the following specification and the claims, the singular forms “a”,“an” and “the” include plural referents unless the context clearlydictates otherwise. As used herein, the term “or” is not meant to beexclusive and refers to at least one of the referenced components beingpresent and includes instances in which a combination of the referencedcomponents may be present, unless the context clearly dictatesotherwise.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” is not limited to the precise valuespecified. In some instances, the approximating language may correspondto the precision of an instrument for measuring the value.

Unless defined otherwise, technical and scientific terms used hereinhave the same meaning as is commonly understood by one of skill in theart to which this disclosure belongs. The terms “comprising,”“including,” and “having” are intended to be inclusive, and mean thatthere may be additional elements other than the listed elements.

As used herein, the term “gamma-prime solvus temperature” refers to atemperature above which, in equilibrium, the gamma-prime phase isunstable and dissolves. The gamma-prime solvus temperature is acharacteristic of a superalloy composition, and is generally measured byDifferential Scanning calorimetry (DSC). The gamma-prime solvustemperature of a superalloy as described herein is in a range of fromabout 2000 degrees Fahrenheit to about 2500 degrees Fahrenheit. In someembodiments, a nickel-based superalloy has the gamma-prime solvustemperature in a range of from about 2100 degrees Fahrenheit to about2400 degrees Fahrenheit, and in some embodiments, from about 2150degrees Fahrenheit to about 2350 degrees Fahrenheit.

Some embodiments of the disclosure are directed to a treatment processincluding heat-treating an article including a superalloy having adegraded microstructure. In some embodiments, the article includes thesuperalloy in single crystal form or directionally solidified form. Insome embodiments, the article including the superalloy has been usedunder the high-temperature service environment. These used articlesinclude degraded microstructure as discussed previously. Such usedarticles may also be referred to as field-returned articles or degradedarticles.

In certain embodiments, the article is cast from a nickel-basedsuperalloy in single crystal form or directionally solidified form. Insome embodiments, a nickel-based superalloy includes from about 7 weightpercent to about 25 weight percent cobalt, from about 4 weight percentto about 25 weight percent chromium, from about 2 weight percent toabout 8 weight percent aluminum, from about 0.5 weight percent to about10 weight percent tantalum, from about 0.1 weight percent to 5 weightpercent niobium, from about 2 weight percent to about 10 weight percenttungsten, from about 1 weight percent to about 8 weight percentmolybdenum, from about 0.0 weight percent to about 6 weight percenttitanium, from about 0.0 weight percent to about 8 weight percentrhenium, from about 0.0 weight percent to about 1.5 weight percenthafnium, from about 0.0 weight percent to about 1 weight percentsilicon, from about 0.0 weight percent to about 0.2 weight percentboron, from about 0 weight percent to about 0.2 weight percent carbon,from about 0 weight percent to about 0.1 weight percent zirconium, fromabout 0 weight percent to about 0.1 weight percent yttrium, and balancenickel. The term, “weight percent”, as used herein, refers to a weightpercent of each referenced element in the nickel-based superalloy basedon a total weight of the nickel-based superalloy, and is applicable toall incidences of the term “weight percent” as used herein throughoutthe specification.

Examples of suitable superalloys include, but not limited to,precipitation hardenable superalloys such as Rene 41® (registeredtrademark of General Electric), the metallic alloy sold under thetrademark GTD-111 (GTD-111 is a registered trademark of General ElectricCompany), the metallic alloy sold under the trademark GTD-222 (GTD-222is a registered trademark of General Electric Company), the metallicalloy sold under the trademark GTD-444 (GTD-444 is a registeredtrademark of General Electric Company) and Rene N5, Rene 80. Rene 104,Rene 108 (Trademark of General Electric Company).

The degraded articles usually include protective coatings such asaluminide coating and thermal barrier coatings. Prior to subjecting suchdegraded articles to the treatment process, a cleaning process may becarried out for removing these protective coatings from the surfaces ofthe degraded articles. Several cleaning procedures known in the art suchas mechanical removal (for example, grit blasting, grinding), water jetmachining, chemical etching etc. can be used for the purpose.

As noted, the treatment process includes heat-treating the article. Theheat-treatment includes subjecting the article to a first heat-treatmentincluding successively heating and cooling the article between a low-endtemperature and a high-end temperature, wherein the low-end temperatureis in a range of from about 1000 degrees Fahrenheit to about 1800degrees Fahrenheit and the high-end temperature is in a range of fromabout 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit, andsubjecting the article to a second heat-treatment at a solutionannealing temperature in a range of from about 80 degrees Fahrenheitbelow a gamma-prime solvus temperature of the superalloy to about 80degrees Fahrenheit above the gamma-prime solvus temperature of thesuperalloy after performing the first heat-treatment. In someembodiments, the treatment process further includes cooling theheat-treated article from the solution annealing temperature.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is stated that a value of a processvariable such as, for example, temperature, pressure, time and the likeis, for example, from 1000 to 1500, preferably from 1100 to 1400, morepreferably from 1200 to 1300, it is intended that values such as 1020 to1485, 1054 to 1430, 1135 to 1370, etc. are expressly enumerated in thisspecification. For values which are less than one, one unit isconsidered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These areonly examples of what is specifically intended and all possiblecombinations of numerical values between the lowest value and thehighest value enumerated are to be considered to be expressly stated inthis application in a similar manner.

In some embodiments, a treatment process 100 for treating an articleincluding a superalloy (as described herein) is described with referenceto FIGS. 3, 4, and 5. As illustrated in FIGS. 3, 4, and 5, the treatmentprocess 100 includes the step 110 of heat-treating the article and thestep 120 of cooling the heat-treated article. The heat-treatment step110 includes the step 102 of subjecting the article to a firstheat-treatment (first heat-treatment step) and the step 104 ofsubjecting the article to a second heat-treatment (second heat-treatmentstep) after performing the first heat-treatment step 102.

The first heat-treatment step 102 may be performed to remove or reducethe residual stresses and dislocation density that had been produced dueto annihilation of the dislocations in the degraded article. As noted,the first heat-treatment step 102 includes successively heating andcooling the article between a low-end temperature and a high-endtemperature. The low-end temperature may vary in a range of from about1000 degrees Fahrenheit to about 1800 degrees Fahrenheit. In someembodiments, the low-end temperature is in a range of from about 1200degrees Fahrenheit to about 1600 degrees Fahrenheit. The high-endtemperature depends on the superalloy composition, and should be lowerthan the recrystallization temperature of the superalloy. In someembodiments, the high-end temperature is in a range of from about 1900degrees Fahrenheit to about 2250 degrees Fahrenheit. In someembodiments, the high-end temperature is in a range of from about 1900degrees Fahrenheit to about 2200 degrees Fahrenheit. In some specificembodiments, the high-end temperature is in a range of from about 1900degrees Fahrenheit to about 2150 degrees Fahrenheit. In some morespecific embodiments, the low-end temperature is in a range of fromabout 1300 degrees Fahrenheit to about 1600 degrees Fahrenheit, and thehigh-end temperature is in a range of from about 1900 degrees Fahrenheitto about 2100 degrees Fahrenheit.

As used herein, the term “recrystallization temperature” refers to atemperature at which the deformed metal grains are replaced by new metalgrains through nucleation and growth.

This successive heating and cooling of the article may be performed oneor more times depending on the extent of mechanical damage and/ordislocation density in the degraded article, and the desirable controlof recrystallization and reduction of the grain size in a rejuvenatedarticle. FIG. 4 illustrates an embodiment where the first heat-treatmentstep 102 includes successively heating and cooling the article one timeprior to subjecting the article to the second heat-treatment step 104.FIG. 5 illustrates another embodiment where the first heat-treatmentstep 102 includes successively heating and cooling the article multipletimes, for example five times prior to subjecting the article to thesecond heat-treatment step 104. The successive heating and cooling thearticle may be performed up to 100 times. In some embodiments, the firstheat-treatment step 102 includes successively heating and cooling thearticle up to 50 times. In certain embodiments, the first heat-treatmentstep 102 includes successively heating and cooling the article from 2times to about 20 times. In some embodiments, the successive heating andcooling the article may be performed 3 times to 15 times for attainingdesirable properties, and in some specific embodiments, from about 5times to about 10 times.

The first heat-treatment step 102 may further include holding thearticle at one or both the low-end temperature and the high-endtemperature for a hold time during the successive heating and coolingsteps. The hold times at the low-end temperature and the high-endtemperature may be up to 5 hours, for example. In some embodiments, thehold times at the low-end temperature and at the high-end temperaturemay range from about 1 minute to about 2 hours. Furthermore, thesuccessive heating and cooling of the article may be performed with thecorresponding heating and cooling rates. In some embodiments, the firstheat-treatment step 102 includes successively heating and cooling thearticle with the corresponding heating rate or cooling rate in a rangeof from about 5 degrees Fahrenheit/minute to about 80 degreesFahrenheit/minute. In some embodiments, the heating rate, the coolingrate or both are in a range of from about 5 degrees Fahrenheit/minute toabout 30 degrees Fahrenheit/minute, and in some embodiments, the ratesrange from about 10 degrees Fahrenheit/minute to about 20 degreesFahrenheit/minute.

In the first heat-treatment step 102, the low-end temperature, thehigh-end temperature, the heating rate, the cooling rate, and the holdtimes at the low-end temperature and the high-end temperature may beidentical or different during the successive heating and coolingstep(s). In some embodiments, the first heat-treatment step 102 includessuccessively heating and cooling between the low-end temperature and thehigh-end temperature. In certain embodiments, the successive heating andcooling occurs between about 1300 degrees Fahrenheit to about 2100degrees Fahrenheit. In some more specific embodiments, the successiveheating and cooling occurs between about 1350 degrees Fahrenheit toabout 2050 degrees Fahrenheit, and in some embodiments to about 2000degrees Fahrenheit. In some embodiments, the first heat-treatment step102 includes cyclically heat-treating the article using at least oneheating and cooling cycle between the low-end temperature and thehigh-end temperature. In some other embodiments, a subsequent heatingand cooling step may have a low-end temperature and a high-endtemperature lower than or higher than that of the previous heating andcooling step. It may be understood (one performing the invention withregard to a particular alloy may well find) that the heating rates andthe cooling rates during the successive heating and cooling steps arenot necessarily identical; and that the low-end and the high-endtemperatures and the hold times are not likewise necessarily identicalin order to achieve a desired result in a desired period.

Following the first heat-treatment step 102, the treatment process 100includes the second heat-treatment step 104. In the secondheat-treatment step 104, the treatment process 100 includes subjectingthe article to the second heat-treatment at a solution-annealingtemperature in a range of from about 80 degrees Fahrenheit below thegamma-prime solvus temperature of the superalloy to about 80 degreesFahrenheit above the gamma-prime solvus temperature of the superalloy.The second heat-treatment step 104 may be performed to partially orfully dissolve the degraded gamma-prime phase in the superalloy. Incertain embodiments, the second heat-treatment step 104 is performed tofully dissolve the degraded gamma-prime phase in the superalloy. In someembodiments, the solution-annealing temperature is in a range of fromabout 60 degrees Fahrenheit below a gamma-prime solvus temperature toabout 60 degrees Fahrenheit above the gamma-prime solvus temperature ofthe superalloy. In some embodiments, the solution-annealing temperatureis in a range of from about 45 degrees Fahrenheit below a gamma-primesolvus temperature to about 45 degrees Fahrenheit above the gamma-primesolvus temperature of the superalloy. The second heat-treatment step 104may be carried out up to 20 hours. In some embodiments, the secondheat-treatment step 104 is carried out for a period of from about 1minute to about 10 hours. In certain embodiments, the period for thesecond heat-treatment 104 is in a range of from about 5 minutes to about4 hours.

After completing the heat-treatment step 110, the treatment process 100further includes the step 120 of cooling the heat-treated article fromthe solution-annealing temperature. In some embodiments, the coolingstep 120 includes cooling the heat-treated article from the solutionannealing temperature to a temperature lower than 2000 degreesFahrenheit. The cooling step 120 may promote the nucleation and growthof the gamma-prime phase and/or the gamma-double-prime phase within themicrostructure of the superalloy. The cooling step 120 may allow forobtaining a cooled article that includes desirable gamma-prime and/orgamma-double-prime phases with desired particle size.

The step 120 of cooling the heat-treated article can be performed with acontrolled manner, for example with a cooling rate greater than 50degrees Fahrenheit/minute. A cooling rate greater than 80 degreesFahrenheit/minute may be desirable because a low cooling rate (e.g.,lower than 80 degrees Fahrenheit/minute) may grow coarse gamma-primephase that may be detrimental for desired mechanical properties.According to some embodiments, the cooling step 120 is performed bycooling the heat-treated article with a cooling rate in a range of fromabout 85 degrees Fahrenheit/minute to about 300 degreesFahrenheit/minute. In yet some embodiments, the cooling rate is in arange of from about 100 degrees Fahrenheit/minute to about 250 degreesFahrenheit/minute. In yet some embodiments, the cooling rate is in arange of from about 120 degrees Fahrenheit/minute to about 220 degreesFahrenheit/minute.

In one embodiment, the cooling step 120 is carried out for cooling theheat-treated article from the solution annealing temperature to about2000 degrees Fahrenheit. In some embodiments, the heat-treated articleis cooled to a temperature between 2000 degrees Fahrenheit and 1000degrees Fahrenheit. In some embodiments, the cooling step 120 isperformed upon cooling the heat-treated article to an aging temperature(e.g., between 1500 degrees Fahrenheit and 2100 degrees Fahrenheit). Insome embodiments, the heat-treated article is cooled to a temperaturelower than 1000 degrees Fahrenheit, and in some embodiments, to roomtemperature. In some embodiments, the cooling step 120 further includesfurnace cooling the heat-treated article to a temperature lower than1000 degrees Fahrenheit after cooling the heat-treated article in acontrolled manner up to a desirable temperature, for example about 2000degrees Fahrenheit. In some embodiments, the heat-treated article iscooled to room temperature.

As used herein, the term “cooled article” refers to an article includinga superalloy received after cooling the heat-treated article asdescribed herein by a cooling rate greater than 50 degreesFahrenheit/minute to a temperature below 2000 degrees Fahrenheit.

Without being limited by any theory, it is believed that the firstheat-treatment that includes successively heating and cooling thearticle, as described herein, annihilates dislocations and significantlyreduces the dislocation density in the mechanically deformed portions ofthe article. This lowering of the dislocation density affects therecrystallization in the mechanically deformed portions of the article(for example, on the surfaces of the article). The reduced dislocationdensity leads to lower recrystallized grain size or no formation ofrecrystallized grains in the mechanically deformed portions during thesecond heat-treatment at the solution-annealing temperature.

In some embodiments, the process further includes aging the cooledarticle. Aging may help in precipitating gamma-prime phase and/or doublegamma-prime phase in desirable particle size. The aging step may beperformed by heating the cooled article at an aging temperature that maybe in a range of from about 1500 degrees Fahrenheit to about 2100degrees Fahrenheit. This aging step may be performed at a combination oftime and temperature to achieve the desired properties. The aging stepmay include heat-treating the cooled article at one or more temperaturesfor a duration of time (for example, >2 hours). Some embodiments includeaging the cooled article by heat-treating the cooled article at a firstaging temperature for a duration of time followed by heat-treating thecooled article at a second aging temperature for a duration of time. Thesecond aging temperature may be lower than the first aging temperature.In some embodiments, the aging further includes heat treating the cooledarticle at a third aging temperature for a duration of time, where thethird aging temperature is lower than the second aging temperature.

The heating rates and the cooling rates, as described herein, during oneor more of the first heat-treatment step 102, the second heat-treatmentstep 104, the cooling step 120 and the aging step, refer correspondinglyto the heating rates and the cooling rates in a direction through amaximum dimension of an article. The maximum dimension may experiencethe slowest heating or cooling rates. In some embodiments, a length, awidth, a radius or a thickness of the article may be the maximumdimension of the article. It will be understood that cooling and/orheating at any rate described herein across the maximum dimension of anarticle provides the most efficient cooling rate and/or heating rate forany article described herein, although there may be instances wherecooling and/or heating across a dimension other than the maximumdimension may be desirable.

In some embodiments, a treated article is received after treating adegraded article by a treatment process as described herein. The treatedarticle may also be referred to as a rejuvenated article. Therejuvenated article may include a microstructure similar to themicrostructure of the originally formed article. That is, the treatmentprocess as described herein enables the recovery of the mechanicalproperties of the originally prepared article while avoiding or reducingthe recrystallization in the mechanically deformed portion of thetreated article. In some embodiments, the treated article exhibits atleast 40 percent of the mechanical properties of the originally formedarticle.

In some embodiments, the mechanically deformed portion includes apopulation of grains (i.e., recrystallized grains) in the surface of thearticle. The population of grains may have an average grain size lessthan 100 microns. In some embodiments, the mechanically deformed portionincludes the population of grains (i.e., recrystallized grains) havingan average grain size in a range from about 1 micron to about 90microns. In some embodiments, the average grain size is in a range offrom about 5 microns to about 80 microns. In some embodiments, thepopulation of grains has a maximum grain size less than 150 microns. Incertain embodiments, the population of grains has a maximum grain sizeless than 125 microns.

Some embodiments of the present disclosure advantageously providereduction in grain size (average grain size<100) of the recrystallizedgrains in the mechanically deformed portions of a rejuvenated articleincluding a SX or DS superalloy, and enables reduced recrystallizationduring the recovery process. Such embodiments thus allow therejuvenation of SX and DS superalloy articles such as turbine bladeswith improved mechanical properties by controlling recrystallization inthe mechanically deformed portions (for example, the machined serrationsof a turbine blade dovetail) of the article during the recovery processand thus reducing or preventing damages in the rejuvenated article forfurther use.

In some embodiments, the treated article may undergo one or morerepairing processes after performing the aging step. The repairingprocesses may include welding and/or brazing for repairing cracks,disposing aluminide coating, and disposing thermal barrier coating (TBC)on the treated article.

EXAMPLES

The following example illustrates methods, materials and results, inaccordance with a specific embodiment, and as such should not beconstrued as imposing limitations upon the claims.

Two components were produced from single crystal Rene N5 that had beenprovided with a standard, proprietary heat treatment. The componentswere exposed to high-temperature service environment for several hours.Component 1 was treated using a control treatment process and component2 was treated using a conventional treatment process. Before undergoingthe treatment processes, components 1 and 2 were processed to strip awaythe aluminide and the thermal barrier coatings.

Example 1: Control Treatment Process

Component 1 was first heated up to a about 2000 degrees Fahrenheit (°F.) with a heating rate of about 10 degrees Fahrenheit/minute (°F./min). After holding the component 1 at about 2000° F. for about 30minutes, the component 1 was cooled to about 1350° F. with a coolingrate about 20° F./min After holding at about 1350° F. for 30 minutes,the component 1 was again heated up to about 2000° F. with heating rateof about 10° F./min followed by holding for about 30 minutes and thenagain cooling to about 1350° F. with the cooling rate of about 20° F./m.These heating and cooling cycles were carried out five times. Aftercompleting five heating and cooling cycles, the temperature was raisedup to a solution annealing temperature that was close to thegamma-solvus temperature (that was measured using DSC) of the Rene N5superalloy with a heating rate of about 10° F./min for the solutionheat-treatment. The component 1 was held at the solution annealingtemperature for about 40 minutes followed by cooling the component 1 toabout 1800° F. with a cooling rate of about 180° F./min followed by astandard proprietary cooling process and aging treatment.

Comparative Example: Conventional Treatment Process

Component 2 was first heated up to about 2000° F. with a heating rate ofabout 10° F./min followed by holding the component 2 at about 2000° F.for about 5 hours. The component 2 was further heated to raise thetemperature up to the solution annealing temperature (as in example 1)with a heating rate of about 10° F./min for solution heat-treatment. Thecomponent 2 was held at the solution annealing temperature for about 40minutes followed by cooling the component 2 to about 1800° F. with acooling rate of about 180° F./min followed by the same standardproprietary cooling process and aging treatment as performed in example1 for component 1.

Testing of Two Components

After the components 1 and 2 had been undergone the treatment processesas described in example 1 and comparative example 2, the microstructuresof components 1 and 2 were then examined in a scanning electronmicroscope (SEM). FIG. 6 shows SEM image of a portion of the component 2that was treated using the conventional treatment process of comparativeexample 2 and FIGS. 7 and 8 show SEM images of two portions of thecomponent 1 that was treated using the control treatment process ofexample 1. It was observed that component 2 after the conventionaltreatment process of comparative example 2 developed a continuous bandof recrystallized grains 10 (FIG. 6) with an average grain size of morethan 100 microns and a maximum grain size of greater than 150 microns.Component 1 that was subjected to the control treatment process ofexample 1 exhibited recrystallized grains of an average grain size of 50microns or less and a maximum grain size of less than 125 microns. Asshown in FIG. 7, certain areas 20 in component 1 were completely devoidof large recrystallized grains as compared to that of the component 2that was subjected to conventional treatment process of comparativeexample 2 (FIG. 6). Furthermore, other areas 30 in component 1 such asthose shown in FIG. 8, exhibited an occasional grain; or a discontinuousor semi-continuous grain growth with an average grain size of less than50 microns.

While only certain features of the disclosure have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the disclosure.

1. A treatment process comprising: heat-treating an article comprising asuperalloy having a degraded microstructure, the heat-treatmentcomprising: subjecting the article to a first heat-treatment comprisingsuccessively heating and cooling the article between a low-endtemperature and a high-end temperature, wherein the low-end temperatureis in a range of from about 1000 degrees Fahrenheit to about 1800degrees Fahrenheit and the high-end temperature is in a range of fromabout 1900 degrees Fahrenheit to about 2250 degrees Fahrenheit; andsubjecting the article to a second heat-treatment at a solutionannealing temperature in a range of from about 80 degrees Fahrenheitbelow a gamma-prime solvus temperature of the superalloy to about 80degrees Fahrenheit above the gamma-prime solvus temperature of thesuperalloy after performing the first heat-treatment.
 2. The treatmentprocess of claim 1, wherein the article comprises the superalloy in asingle crystal form or directionally solidified form.
 3. The treatmentprocess of claim 1, wherein the low-end temperature is in a range offrom about 1300 degrees Fahrenheit to about 1600 degrees Fahrenheit andthe high-end temperature is in a range of from about 1900 degreesFahrenheit to about 2100 degrees Fahrenheit.
 4. The treatment process ofclaim 1, wherein the first heat-treatment comprises successively heatingand cooling the article up to 50 times.
 5. The treatment process ofclaim 1, wherein the first heat-treatment comprises successively heatingand cooling the article from 2 times to about 20 times.
 6. The treatmentprocess of claim 1, wherein the successive heating and cooling iscarried out with a corresponding heating rate or cooling rate in a rangeof from about 5 degrees Fahrenheit/minute to about 80 degreesFahrenheit/minute.
 7. The treatment process of claim 1, wherein thesuccessive heating and cooling is carried out with a correspondingheating rate or cooling rate in a range of from about 10 degreesFahrenheit/minute to about 50 degrees Fahrenheit/minute.
 8. Thetreatment process of claim 1, wherein the second heat-treatment iscarried out up to 20 hours.
 9. The treatment process of claim 1, whereinthe second heat-treatment is carried out for a duration of time in arange of from about 5 minutes to about 5 hours.
 10. The treatmentprocess of claim 1, wherein the second heat-treatment is carried out ata temperature in a range of from about 45 degrees Fahrenheit below thegamma-prime solvus temperature of the superalloy to about 45 degreesFahrenheit above the gamma-prime solvus temperature of the superalloy.11. The treatment process of claim 1, further comprising cooling theheat-treated article from the solution annealing temperature.
 12. Thetreatment process of claim 11, wherein the cooling of the heat-treatedarticle is carried out with a cooling rate higher than 50 degreesFahrenheit/minute.
 13. The treatment process of claim 12, wherein thecooling rate is in a range of from about 80 degrees Fahrenheit/minute toabout 300 degrees Fahrenheit/minute.
 14. The treatment process of claim12, wherein the cooling rate is in a range of from about 100 degreesFahrenheit/minute to about 250 degrees Fahrenheit/minute.
 15. An articlereceived after performing the treatment process in accordance withclaim
 1. 16. The article of claim 15, wherein a mechanically deformedportion of the article comprises a population of grains having anaverage grain size less than 100 microns.
 17. The article of claim 16,wherein the population of grains has an average grain size in a range offrom about 1 micron to about 90 microns.
 18. The article of claim 16,wherein the population of grains has a maximum grain size less than 150microns.
 19. The article of claim 18, wherein the population of grainshas a maximum grain size less than 125 microns.
 20. A treatment processcomprising: heat-treating a single crystal or directionally solidifiedarticle of a nickel-based superalloy comprising a degradedmicrostructure, the heat-treatment comprising: subjecting the article toa first heat-treatment comprising successively heating and cooling thearticle at least 2 times between a low-end temperature and a high-endtemperature, wherein the low-end temperature is in a range of from about1300 degrees Fahrenheit to about 1600 degrees Fahrenheit and thehigh-end temperature is in a range of from about 1900 degrees Fahrenheitto about 2100 degrees Fahrenheit; subjecting the article to a secondheat-treatment at a solution annealing temperature in a range of fromabout 80 degrees Fahrenheit below a gamma-prime solvus temperature ofthe superalloy to about 80 degrees Fahrenheit above the gamma-primesolvus temperature of the superalloy after performing the firstheat-treatment; and cooling the heat-treated article from the solutionannealing temperature with a cooling rate higher than 50 degreesFahrenheit/minute.